linux-kernel - [PATCH] io_uring: unregister eventfd while holding lock when freeing ring ctx

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Message-Id: <20220207105040.2662467-1-usama.arif@bytedance.com>
Date:   Mon,  7 Feb 2022 10:50:40 +0000
From:   Usama Arif <usama.arif@...edance.com>
To:     io-uring@...r.kernel.org, axboe@...nel.dk, asml.silence@...il.com,
        linux-kernel@...r.kernel.org
Cc:     fam.zheng@...edance.com, lkp@...ts.01.org, lkp@...el.com,
        Usama Arif <usama.arif@...edance.com>,
        kernel test robot <oliver.sang@...el.com>
Subject: [PATCH] io_uring: unregister eventfd while holding lock when freeing ring ctx

This is because ctx->io_ev_fd is rcu_dereference_protected using
ctx->uring_lock in io_eventfd_unregister. Not locking the function
resulted in suspicious RCU usage reported by kernel test robot.

Reported-by: kernel test robot <oliver.sang@...el.com>
Signed-off-by: Usama Arif <usama.arif@...edance.com>
---
 fs/io_uring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index ad8f84376955..dbc9d3f3f6c5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -9471,8 +9471,8 @@ static __cold void io_ring_ctx_free(struct io_ring_ctx *ctx)
 		__io_sqe_files_unregister(ctx);
 	if (ctx->rings)
 		__io_cqring_overflow_flush(ctx, true);
-	mutex_unlock(&ctx->uring_lock);
 	io_eventfd_unregister(ctx);
+	mutex_unlock(&ctx->uring_lock);
 	io_destroy_buffers(ctx);
 	if (ctx->sq_creds)
 		put_cred(ctx->sq_creds);
-- 
2.25.1